Answer this question truthfully
### Question: What causes Headache?
### Response: Headache is a kind of symptom, the most important thing is to make the underlying causes clear.
Meidcal history, the characteristics of the patient's headache. Physical examination and neurological evaluation. Eye examination: It is very useful to identify underlying problem in the brain. Blood tests: Blood tests include complete blood count, liver, and kidney function tests. The results of the various lab tests may provide clues to detect some secondary headaches that can cause coma. Head imaging studies such as CT and MRI: These images can be used to detect the structural problems in the brain. Electroencephalography (EEG): This test can demonstrate the electrical activity in the brain and be helpful for the diagnosis.